As industries have been rapidly developed and advanced, an automated manufacturing system is evolving fast than ever. With the development of industries, a conventional automated manufacturing system needs to be changed into a new automated manufacturing system, and the delay of introduction of a new automated system may incur a great loss of profit and credibility of a manufacturer.
Various automated equipment which constitute an automated manufacturing system are controlled and operated by a programmable logic controller (PLC). The PLC stores therein ladder diagram information as a control program in the form of Boolean logic.
Pieces of automated equipment of the automated manufacturing system are operated by PLC output signals output from the PLC. The process state during operation or after operation may be monitored by a sensor and transmitted to the PLC in the form of a PLC input signal. The PLC input signal is a signal containing information on the updated process state.
The PLC performs internal logic operation in response to the PLC input signal to output a PLC output signal. The PLC output signal is a signal that instructs pieces of automated equipment to perform the next process according to the updated process state. The automated equipment performs processes, which accord with the updated process state, in response to the PLC output signal.
To run an automated manufacturing system in practice, a process control operator may manually write a control program for the automated manufacturing process by including PLC code, and make a test run of the control program by applying it to real equipment of the system. However, since the control program may have inherent human error, the manufacturing control operator needs to test the automated manufacturing system prior to the test running with respect to ladder diagram that includes the PLC code.
For quick introduction of an automated manufacturing system, it is general to test the automated manufacturing system, and control engineers thus have paid growing attention to control program test for the automated manufacturing system. In addition, control program verification after satisfactory design of PLC is a prerequisite for introducing an automated control system.
As an example of a simulation method for verification of PLC code that controls a plurality of lines in the automated manufacturing system, lines of the automated manufacturing system are divided on the basis of a unit of PLC control and simulation is performed for verification of individual software PLC code corresponding to each PLC control unit as shown in FIG. 1. As another example, an OLE for process control (OPC) server and a plurality of hardware PLCs are connected to each other for OPC communication and simulation is performed for PLC code verification in units of lines through the OPC communication as shown in FIG. 2.
Referring to FIG. 1, a PLC simulation program uses an input/output model that defines operational characteristics of field equipment as discrete events and a graphic model that defines operation states of the field equipment in an effort to verify whether a logic operation is normally performed in response to PLC input/output signals communicated with a software PLC.
Referring to FIG. 2, a plurality of hardware PLCs which control lines of an automated manufacturing system form a network, input/output code signal values of individual hardware PLCs are integrated and registered in the OPC server, and the registered input/output code signal values are associated with a PLC simulation program to verify whether to perform an independent logic operation in each PLC or whether to perform a logic operation with respect to other hardware PLCs.
However, in the simulation method shown in FIG. 1 in which the lines of the automated manufacturing system are divided on the basis of a unit of PLC control and simulation is performed for verification of individual software PLC codes that correspond to each PLC control unit, the automated manufacturing system that controls a plurality of the lines and the equipment cannot be implemented as software because the simulation for code verification is allowed to be performed by each PC for only one software PLC according to a PLC vender type. Moreover, the aforementioned simulation method in which the verification of one software PLC code is performed by one PC cannot verify errors and abnormal states which may occur during communication of input/output signals between each software PLC and human machine interface (HMI) in an actual automated manufacturing system that consists of a network of PLCs.
On the other hand, in a case where a plurality of the hardware PLCs are connected to the OPC server and simulation is performed for PLC code verification in units of lines as shown in FIG. 2, control logic configuration based on a plurality of the hardware PLCs may allow the PLC control simulation in units of lines, while environment settings for the PLC control simulation are complex and cost for PLC code verification is increased due to a communication environment established by a plurality of the hardware PLC and the OPC server.